1. Field of the Invention
The present invention relates to a laser beam scanning system equipped with a laser beam modulation (intensity) controller and laser beam deflector.
2. Description of the Related Art
In general, an optical device made of a substance medium, such as an optically anisotropic crystal, liquid crystal or conductive glass, is known as a laser beam modulation (intensity) controller and laser beam deflector, and hence as a control means for a laser beam scanning system, in terms of its structure, operation stability and controllability.
The laser beam intensity controller and laser beam deflector for the aforementioned substance medium unavoidably reveal a non-linear optical characteristic upon receipt of a control input. Upon deflecting a laser beam by, for example, a laser beam deflector, the laser beam deflector manifests the diffraction efficiency of non-linear character with respect to the deflection angle as shown in FIG. 1. In the graph shown in FIG. 1, the abscissa shows the deflection angle and the ordinate the diffraction efficiency. As seen from the graph, the diffraction efficiency varies depending upon the deflection angle and a laser beam emerging from the laser beam deflector varies in intensity depending upon the laser beam radiation position. It is, therefore, impossible to obtain an "as-controlled" beam intensity and either to illuminate a whole illumination surface with a laser beam of uniform intensity.
Furthermore a driver for the laser beam deflector has also a non-linear characteristic in general so that the laser beam is linearly not deflected for an instruction signal. A driver signal corresponding to a pattern as indicated by a in FIG. 2A, even if being applied to the laser beam deflector, is deformed into a pattern as indicated by b in FIG. 2B. It is, therefore, impossible to measure an accurate measurement even if such a laser beam scanning system is used for a measuring device such as a wafer probing apparatus using a laser beam. The measurement by using a probe is critical for a high density integrated circuit of for example 4M, 16M, or more bits. The laser probes has characteristics to measure such an integrated circuit, so that the deformation of a pattern is not avoidable for a laser probe.